High Harmonic Fast Wave Experiments on TST-2
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Transcript of High Harmonic Fast Wave Experiments on TST-2
High Harmonic Fast Wave Experiments on TST-2
Y. Takase, A. Ejiri, S. Kainaga, H. Kasahara1), R. Kumazawa1), T. Masuda,
H. Nuga, T. Oosako, M. Sasaki, Y. Shimada, F. Shimpo1), J. Sugiyama,
N. Sumitomo, H. Tojo, Y. Torii, N. Tsujii, J. Tsujimura, T. Yamada2)
12th International Workshop on Spherical Torus 2006 Chengdu
11-13 October 2006
University of Tokyo, Kashiwa, 277-8561 Japan1)National Institute for Fusion Science, Toki, 509-5292 Japan2)Kyushu University, Kasuga, 816-8580 Japan
• TST-2 spherical tokamak and RF system
• HHFW experiment– Electron heating experiment– Wave diagnostics
• RF magnetic probes• Reflectometry
– Wave measurements• parametric decay• scattering
– TORIC full-wave analysis
• EC start-up experiment
• Plans – 200MHz experiments on TST-2– RF sustainment of high plasmas in UTST
Outline
TST-2 Spherical Tokamak
ECH: 2.45GHz (< 5 kW)HHFW: 21MHz (< 200 kW x 2)
ECH
HHFW
R / a = 0.38 / 0.25 m (A = 1.5)
Bt = 0.3 T / Ip = 0.1 MA
21 MHz Matching/Transmission System
• RF power
400 kW
• Frequency f = 13, 21, 30 MHz (/H ~ 7 at BT = 0.2 T, f = 21 MHz)
• Toroidal wavenumber k = n/R0 = 11, 16, 26 m-1
(n = 4.3, 6, 10)
varied by changing the strap spacing
• Faraday shield angle ~ 30°
currentstraps(0, )
Mo limiters
Faraday shield
Variable k Two-Strap Antenna
Single-pass Absorption Calculation
• Single-pass absorption is greater for double-strap excitation
• Single-pass absorption– increases with ne
– increases with Te
– decreases with Bt
(increases with e )
0.0
2.0
4.0
6.0
8.0
10
0.0 5.0 10 15 20 25 30
ne dependence for single and
double strap excitations
Single strap[%] Double strap[%] Single strap[%] Double strap[%] Single strap[%] Double strap[%]
Sin
gle
pas
s ab
sorp
tion
[%]
Toroidal mode number
Te = 300 eV
BT = 0.2 T
5.0x1019 m-3
1.0x1019 m-3
3.0x1019 m-3
double-strap
single-pass absorption
== 0.18
ELD + TTD
ELD + TTD + CROSS
ELD
ELD + CROSS
Imag ( k⊥)
dxke
)Im(21
Bt = 0.15 T ne = 1.0×1019 m-3
Te = 100 eV n = 10
Single-Pass Absorption Improves with e
• Analysis of HHFW heating scenarios used on TST-2 is being carried out using the TORIC full-wave code.
Bt = 0.2 T, f = 21 MHz, n = 10, ne0 = 2 1019 m-3, Te0 = 0.2 keV
TORIC Full-Wave Calculations
Electron absorption: 100%
• Soft X-ray increased, but density and radiated power did not change electron heating
• Strongest response near plasma center
t (ms)
Ip
nel
Prad
SX (> 200 eV)
360 kW RF
Electron Heating by HHFW
Low
field
sid
eH
igh fi
eld
sid
e
~ R0
180kW360kW
no HHFW
R=0.19m
R=0.26m
R=0.38m
R=0.43m
R=0.54m
Center
PS noise
• Increases in stored energy and visible-SX emission are greater for double-strap excitation
– Consistent with single-pass absorption calculation
Single-Strap vs. Double-Strap Excitation
double-strapsingle-strap
no RF
with RF
Edgeemission
visible-SXemission(A.U.)
PNET = 120 kW PNET = 120 kW
• RF magnetic probes– Sensitive to electromagnetic component
– Plasma edge only
• Reflectometry– Sensitive to electrostatic component
– Can probe the plasma interior
• Both parametric decay instability (PDI) and frequency broadening due to scattering by density fluctuations were observed.– These processes can alter the wavenumber spectrum, and affect bot
h wave propagation and absorption.
Wave diagnostics on TST-2
φ= -60°
φ= -30°
φ= -55°φ= -65°
φ= -115°
φ= -120°
φ= 155°φ= 150°
φ= 145°
φ= 65°φ= 60°φ= 55°
φ= 30°
φ= 0°
Top viewS.S. enclosure
Slit
Core (insulator)
1-turn loop
Semi-rigid cable
2cm
Direction ofB field to bemeasured
RF Magnetic Probes at 14 Toroidal Locations
toroidal direction
Bz B
φ= 9°
φ= -9°
φ= -125°
B
RF21MHz
eit
One of three sources is used Frequency sweepable VCO for profile measurements Fixed Gunn Osc. (25.85 or 27.44 GHz) for RF measurements
Ep x Bt
Aeit
Aeit+i
I
cos(p+t+RF)
sin(p+t+RF)
VCO6-10GHz
X4
QLO RF
coaxial waveguidescalar horn
Digitizer or Oscilloscope
<250MHz sampling
F.G.
X5
X10
Gunn25.85 or 27.44 GHz
D.C.-3dB
5-20mW
DC-500MHz
24-40GHz100mW
TST-2 Reflectometer System
Window200
TFCoil
TST-2V.V.
Mirror
Mirror
HornAntennas
Microwave Reflectometer
Most probable decay process:
High Harmonic Fast Wave (HHFW)
Ion Bernstein Wave (IBW)+
Ion-Cyclotron Quasi-Mode (ICQM)
Magnetic field dependence
H at outboard edge
Threshold power ~ 20 kW
High power
Lowpower
Parametric Decay: FW IBW + ICQM
Parametric Decay Instability (PDI)
PDI
①
②
probe②
RF probe
1.8 MHz
HHFW250 kW
Time [s]
Reflectometer25.85 GHz (cosine)
Reflectometer25.85 GHz (sine)
RF Probe (dB/dt)Antenna Limiter, P12
Frequency [MHz]
Comparison of RF Probe and Reflectometer Spectra
QMIBW
Comparison of RF Probe and Reflectometer Spectra
Reflectometer (cos)
Reflectometer (sin)
RF Magnetic Probes
f (MHz)
FW ?
IBW
QMIBW
noise (Al reflector)
2510 20
0
-20
-40
-60
-800
P (dB)
0
-20
-40
-60
-80
P (dB)
0
-20
-40
-60
-80
P (dB)
155
PDI becomes stronger as the plasma outer boundary approaches the antenna
Rout
Dependence on Plasma Position
antennalimiter
①
②
③
④
① ②
③ ④
Outboard vs. Inboard Comparison
• Inboard spectrum similar to outboard, but weaker
RF probes
φ= 21°straps
φ= 39°
R=125 R=630mmR=700mm
Z = 0mm
Z = -150mm
port10
①
②③
④
① ②
③ ④
• Broadened spectrum is only weakly dependent on vertical position
midplane B
midplane Bz
Z = 150mm
Inboard Side Spectra
RF probes
Vacuum Plasma
① ①
② ②
Frequency broadening of the pump waveby the plasma is observed.
Possible processes:
• Parametric decay• Scattering by density fluctuations
Frequency Broadening
①
②
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
7.0 7.5 8.0 8.5 9.0
ch1ch4ch3ch2
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
7.0 7.5 8.0 8.5 9.0
ch1ch4
ch3ch2
f (HHFW)Pump wave power
0
0.0005
0.001
0.0015
0.002
0.0025
7.0 7.2 7.4 7.6 7.8 8.0 8.2 8.4 8.6 8.8 9.0
ch1ch4ch3ch2
Lower sideband power
①
②
③
④
0
0.5
1
1.5
2
2.5
7.0 7.5 8.0 8.5 9.0
R = 195
R = 260
R = 370
SX / SX
Density Dependence Varies with Probe Position
10dBf (HHFW)
• PDI is generally reduced at high density
• Only weak effect on heating
Preliminary
nelnel
• A k|| variable antenna was installed in TST-2, and the RF power capability was increased to 400kW. – Dependence on k|| spectrum (same spectral shape but different k||)
will be studied.– Single-pass absorption is expected to change from 10% to 35% wh
en ne0 = 3.01019 m−3 and Bt = 0.3T.
• In electron heating experiments, soft X-ray emission increased with RF power.– Stored energy increase was larger for double-strap excitation. – More direct measurement of Te is necessary (TS in preparation).
• Analysis of HHFW scenarios used on TST-2 is being carried out using TORIC.
Summary (HHFW Heatng)
• PDI and frequency broadening due to scattering were observed by RF magnetic probes.– The strength of PDI increased as the outer boundary of the plas
ma approached the antenna.
– Density dependence varies with RF probe location.
– Parametric decay became weaker at high densities where single-pass absorption is predicted to become stronger.
– The effect of parametric decay on plasma heating is not clear.
• Initial results of RF wave detection inside the plasma by microwave reflectometry were obtained.– PDI spectrum clearly observed
– Differentiation of ES and EM components may be made.
Summary (RF Measurements)
EBW Heating on TST-2@K (2003)
(dW/dt) indicates Pabs/Pin > 50% when ne in front of antenna is steep enough
Thursday: S. Shiraiwa, et al.,“Study of EBW Heating on TST-2”
< 200 kW@ 8.2 GHz
Typical EC Start-up Discharge
(a) Bt decreases gradually. (RECH decreases gradually.)
(b) IPF is kept constant.
(c) PEC is kept constant.
(d) Ip increases with time, but disappears when the = e layer moves out of the vacuum vessel.(up to 0.5 kA produced by 4 kW)
(e) ne is almost constant near the cutoff density.
0.00
0.25
RE
CH
[m
]
(a)
0
3
PF
2co
il c
urr
ent
[kA
] (b)
0
5
PE
CH
[k
W]
Forward
Reflection
(c)
0
0.2
0.4I p
[k
A]
(d)
0
6
12
10 20 30 40 50 60NL
[10
16m
-2]
Time [ms]
(e)
inboard limiter
Previously achieved: 1kA/1kW (2.45GHz) 4kA/100kW (8.2GHz)
Dependence on power and resonance position
0
0.1
0.2
0.3
0.4
0.1 0.15 0.2 0.25 0.3
#43371#43372
I p [
kA]
RECH
[m]
Diameter of the CS
0.0
0.1
0.2
0.3
#43371#43372
RE
CH
[m
] (a)
0.0
0.1
0.2
0.3
0.4
0 10 20 30 40 50 60 70
I p [k
A]
Time [ms]
(b)
0
0.1
0.2
0
5
10
0 1 2 3 4
I p [
kA
]
NL
[1016
m-3
]
PNET
[kw]
Ip depends on the = e resonance position (RECH).
Ip increases with PEC, whereas ne saturates around the cutoff density7 1016 m-3 [NL = (5-6) 1016 m-3].
time
inboardlimiter
Dependence on PF Strength and Decay Index
PF2+PF5 PF1PF2PF31m
-1m0.1m 0.7m
Mirror ratio
0
0.1
0.2
0.3
0.4
0 0.2 0.4 0.6 0.8 1 1.2
PF3PF2&PF5PF2PF1
I pm
ax [
kA
]
Bz [mT]
• Ip maximizes at a certain field strength.
• Highest Ip is achieved with PF2 (medium decay index).
Effect of HHFW Injection
3 cases are compared:
● ECH only
● ECH + HHFW
● ECH turned off during HHFW
0
5
PE
CH
[k
W] Forward
Reflection
(b)
0.0
0.1
0.2
RE
CH
[m
]
RCS
(a)
0.0
0.3R
adia
tion
[a.u
.](e)
0
0.1
0.2
0.3
0.4
#42904#42905#42915
I p [k
A]
(d)
0
10#42904#42905
PH
HF
W [
kW
]
(c)
Net Power
0
4
8
10 20 30 40 50
NL
[10
16m
-2]
Time [ms]
(f)
• Ip responds quickly to HHFW
• ne and Prad increase during HHFW
• After ECH turn-off, Ip decays and HHFW reflection increases.
Single Particle Orbit Analysis
• Phase space for confined orbits is large for low A devices.
• Orbit-averaged toroidal precession is co-directed for all confined orbits.
(c) ctr trapped(b) co trapped(a) circulating
0.1 0.8 m-1
+1
Confined region in phase space(inside outermost blue boundary)
(b)
(a)(c)
V||/V0
V /V0
0
1
-0.4 0 1.2
Electron orbits starting from R = 0.38m / Z = 0m
Velocity is normalized by V0=Rsp
(p is the cyclotron frequency corresponding to Bp)
A. Ejiri, et al., to be published.
Driven Current Based on Single Particle Analysis
LMINS
LMINScurv
e
e
pse
RRR
ZZRR
F
FmkT
Renj
,2
Max ,12
32)( where
)(2
2
1~
2max
2max
2/32
2
3
3
Under a low Te (or high BZ) approximation (VTe << V0), j is given by
)( 34F
RR
B
Bp
Sp
p
)(~ 3 FBRp
jpS
This current has the same parameter dependence and the same order of magnitude as pressure driven currents
The generated field is
where R is the thickness of the EC deposition layer
Comparison with Experiment
0
0.1
0.2
0.3
0.4
0 0.2 0.4 0.6 0.8 1 1.2
PF3PF2&PF5PF2PF1
I pm
ax [
kA
]
Bz [mT]2
/[mT] 5.0
ee
pSz
mT
RB
• Bz dependence agrees qualitatively with experiment.
• Dependence on PF curvature is different.
• Predicted current for PF3 is negligibly small.
Assuming correspondence of Ipmax for PF2
[eV] 200~eT
0
0.1
0.2
0.3
0.4
0 1 2 3 4 5 6
<d/
dt>
RS/(
Te/m
e)1/2
RS
p/(T
e/m
e)1/2
PF1
PF2
PF2+PF5PF1 (Analytic)
,1~)( ],[m 10
[m], 01.0 [m], 4.0
3317
max
Fn
RZ
e
Further assuming
][kA 4.0~pI
estimate for driven Ip is
Conclusions (EC Start-up)
• Ip of up to 0.5 kA was obtained by ECH start-up (2.45 GHz / 4 kW) .
• Ip increases with the decrease in Bt.
• Highest Ip was achieved with PF configuration with medium index and appropriate field strength.
• Ip and ne increase with PEC, but ne saturates around the cutoff density.
• Ip increased by up to 0.4 kA by addition of HHFW power.
• Analytic expressions for generated current were derived based on single particle orbits:
– Generated current has a similar form to pressure driven currents. – Self-field generation becomes siginificant at high p.
• The proposed model and experimental results are not inconsistent, but further theoretical and experimental studies are needed.
Preparation in Progress for 200 MHz Experiments
E
Bt = 0.3 T, f = 200 MHz, n = 10, ne = 2 1018 m-3, Te = 0.3 keV
Full-wave calculation by TASK/WM
TST-2200 MHz transmitters (from JFT-2M)
Combline antenna (GA)
UTST
• HHFW (~ 20 MHz)• LHFW (~ 200 MHz)
TS-3 / TS-4
TST-2
UTST
A New Ultra-High ST Based on Plasma Merging
Merging scenario
Tokyo
Formation of ultra-high ST plasma using plasma merging
Sustainment using innovative RF methods
Friday: Y. Ono, et al., “Initial operation of UTST High-Beta Spherical Tokamak Merging Device”